In code division multiple access (CDMA) communication systems compatible with IS-95, both a source and target base-station are on the same frequency during hard handoff. Since the elements comprising the signaling at the signaling layer (typically Layer 2, or L2) are disparate between source and target base-stations, the mobile station is instructed to reset it's L2 acknowledgment procedures in a Handoff Direction message sent to the mobile station by the source base-station. In this situation, there exists a time period when the target base-station may acquire the mobile station before the mobile station is instructed to handoff (via the Handoff Direction message) from the source to the target base-station. During this time period, the mobile station may send a message which would be received by the source base-station and may be received by the target base-station. Additionally, the mobile station may send a message to the target base-station before it sends a Handoff Completion message to indicate it has completed handoff.
Within the L2 signaling layer, there exists mechanisms which insure the delivery of a message to the base-station or the mobile station via message sequence numbers, acknowledgment sequence numbers, a retransmit mechanism, and a duplicate message detection mechanism. Given the above problems associated with same frequency hard handoff, i.e., inter alia, that the first message received by the target base-station may not be intended for the target base-station and that the first message sent to the target base-station by the mobile station may not be a Handoff Completion message, failures which are likely to occur include the duplicate message detection mechanisms erroneously discarding valid messages and the acknowledgment window size growing beyond four messages as specified in IS-95. An additional problem presented by the above scenario is that a base-station (source or target) can get into a state where it does not acknowledge future messages.
Thus, a need exists for an efficient method for mitigating the problems associated with the prior art.